The quality and behavior of beer foam are essential characteristics of the visual appearance of beer, which has an influence on the consumer behavior. Foam quality is mainly determined by its stability, which is a standard quality control parameter in most breweries. Another foam quality sometimes tested, though more difficult to quantitatively determine, is that of the cling or lacing, which is the foam that attaches to the wall of glass container after the foam collapses. Other criteria which mark the quality are color, bubble size and variation of bubble size, taste as well as how the foam collapses over time. It is advantageous to have a more stable head of foam on a beer after being poured into a glass container; this characteristic is referred to as the foam stability, similarly advantageous to have more foam cling (or lacing). For many years it has been known that hops improve the foam stability and cling (or lacing) of beer and that it is the isomerized alpha-acids that are the major contributor to the improved foam stability and lacing (L. R. Bishop et al. J. Inst. Brew. 80, 68-80, 1974). Reduced, isomerized hop acids (tetrahydroiso- and hexahydroiso-alpha-acids) have been discovered to improve foam stability and cling (lacing) of beer at lower concentrations than the iso-alpha-acids; this is especially important with the low bitterness lagers in which the low concentrations of the iso-alpha-acids would not allow for a good and stable head of foam. Many brewers would rather use a natural product for their beers (that is formed by a natural process, rather than by catalytic hydrogenation), however except for the hop pectins, most other foam-stabilizing hop compounds are not naturally formed in hop products, nor formed by a natural process. A partially hydrogenated or dihydro-alpha-acids has been reported to form naturally in hop products and its isomerized product has been shown to improve foam stability and lacing (R. J. Smith, D. Davidson, and R. J. H. Wilson J. Am. Soc. Brew. Chem. 56, 52-57, 1998). Another disadvantage of using the tetrahydroiso-alpha-acids is that some brewers do not like the “unnatural”, almost “hockey-puck” appearance of the foam after collapse,
There has been a report that the alpha-acids improve the beer head formation similar to that of the iso-alpha-acids, though the lowest concentration tested was about 26 ppm (K. Asano and N. Hashimato in Rept. Res. Lab. Kirin Brewery Co., Ltd., No. 19, 9-16, 1976) and it did not address whether the alpha-acids improve foam stability of beer. There has also been one report to state that the alpha-acids are equally as effective as the iso-alpha-acids in improving the lacing (or cling) of beer, though no quantitative results were provided (C. W. Banforth and G. Jackson in European Brewery Convention, Proceedings of the 19th Congress 1983, 331-338).
Alpha-acids, in the form of hops, hop pellets, and various extracts have for many years been added to the kettle boil to transform, or isomerize, the low bittering, alpha-acids to strongly bitter, iso-alpha-acids (even though these compounds are isomers, they have quite different chemical properties due to structural differences between the molecules). Because of the slow isomerization of the alpha-acids at the pH of aqueous malt extract during the kettle boil, some of the alpha-acids remain after the boil. Most of the residual alpha-acids are subsequently removed from suspension by binding to the yeast during fermentation and the accompanying drop in pH as well as decrease in temperature during lagering which further reduces the solubility of the alpha-acids such that most commercial, lager beers have quite low concentrations of alpha-acids of less than 1 ppm. In order to have a reasonably good utilization of the alpha-acids in beer, the alpha-acids need to be added after most of the yeast has been removed (referred to as post-fermentation). Some commercial samples of ales can have concentrations of alpha-acids in the range of 2-8 ppm. These relatively high concentrations of alpha-acids are due to addition of hops or hop pellets either late in the kettle boil, in the whirlpool, or after fermentation by a process known as dry hopping. The reason for the addition of these hop products have been to add hop oils and hoppy aroma/flavor to ales and has been quite popular with many of the craft brewers. There has been no evidence to suggest that these higher concentrations of alpha-acids result in improved foam stability or cling (or lacing).
We have discovered that stable solutions of purified and completely natural alpha-acids (in which most of the beta-acids, hop oils and waxes/fats have been removed) can be added to beer after fermentation, with good utilization, and without changing the bittering or flavor profile of the beer, so as to improve the foam quality (including stability and lacing or cling) of beer and that the alpha-acids are more effective than the iso-alpha-acids at improving the foam stability and lacing of the beer and are only slightly less active than the unnatural, hydrogenated iso-alpha-acids. Another advantage of using the alpha-acids is that foam appears to be more “natural-looking” than the beer foam with tetrahydroiso-alpha-acids. Another advantage of the alpha-acids is that they are not bitter (at least to a concentration of 14 ppm in beer, A. Fritsch and T. H. Shellhammer J. Am. Soc. Brew. Chem. 65, 26-28, 2007), so foam stability of beer can be improved without changing the bittering and flavor profile of the beer. In this invention we also describe hop products consisting of solutions of alpha-acids, as well as solutions of alpha-acids which have another hop acid and/or co-solvent which further improves the physical and/or chemical stability of the hop product. We also describe processes for making these hop products.